Poultry
(turkey, duck and chicken) slaughtering and processing plants
typically process 20,000 or more birds per day. The shackling,
killing, scalding, and picking areas of the plant emit airborne
microorganisms, moisture, and dust. These contaminants are
unwanted in the processing and packing areas of the plant
because they can affect product quality and safety. They also
pose a potential threat to the health and well-being of the
workers in the plant.

Typical
Ventilation Systems

Poultry
slaughtering plants are typically ventilated with negative-pressure
systems. Most of the air moving capacity is provided by large
roof fans above the scalding and picking equipment. The balance
of the air is moved with local exhaust fans in other locations.
This ventilation strategy is based on the theory that fresh
air will flow one-way from relatively clean meat cutting and
packaging operations to locations with bioaerosol (bacterial
pathogens and spoilage microorganisms) emission and finally
to the exhaust fans, Figure 1. However, they do not always
achieve this desired airflow pattern. The following aspects
of the ventilation system are critical for achieving the desired
airflow pattern.

Fresh
Air Intakes

The distribution
of air in any ventilated room depends on the size and location
of ventilation intakes. In a poultry plant, many rooms are
ventilated with air entering and leaving wall openings, Figure
1. These wall openings consist of shackle line openings and
doorways. Shackle line openings are for transfer-ring product
from one processing operation to another. Doorways are for
the convenience of worker and vehicle traffic. Room ventilation
is apparently not considered when these wall openings are
located. However, their sizes and locations have a significant
impact on room air distribution.

Figure 1. Schematic of air movement in a poultry slaughtering
plant.

With
a negative pressure system, air leaks into the room around
doorways and other unplanned openings. Many doors in poultry
plants consist of double doors, large garage doors, doors
to walk-in coolers, and shipping/receiving docks. These large
doors can have crack areas with up to 500 cfm flowing through
them. Cold air leaking into a room due to negative pressure
makes occupants uncomfortable and can cause considerable condensation
and frost as warm moist air mixes with weak cold air jets
nd contacts cold surfaces. The plant's largest exhaust fans
are located in relatively small picking and scalding rooms
and move about 12,000- to 50,000- cfm. These fans create a
large negative static pressure that draws in air from all
openings to the room. Much of the air flows inward from the
line openings to the outside shackling area, typically 30
to 90% of the exhaust airflow. The rest of the air comes in
from the plant, Figure 1. The overall room air balance is
influenced by the size of he openings to the room. More air
could be drawn through the plant if the openings into the
shackling area were reduced and the openings to the evisceration
room were enlarged. Consult a ventilation engineer for help
in determining best opening sizes.

Arbitrary
Modifications

The original
ventilation system for a poultry processing plant is sometimes
modified as rooms are added for more processing capacity.
Additionally, exhaust fans are sometimes added in attempts
to eliminate condensation. These exhaust fans can move air
opposing the main exhaust fans in the picking and scalding
rooms. Air movement from clean areas to bioaerosol emission
sources can be reversed if enough fans are added.

A plant
has three fans in the scalding room with a total capacity
of 50,000 cfm, Figure 2a. However, 30,000 cfm is drawn through
large line openings from the outdoor shack-ling area which
is immediately adjacent to the scalding room. The remaining
20,000 cfm is drawn through line openings from the eviscerating
room. Therefore, the original design causes 20,000 cfm to
flow through the plant from the processing rooms to the eviscerating
area and then to the scalding and picking room. A year later,
the plant adds three, 4,000 cfm fans in the packaging room
to eliminate moisture, and prevent condensation occurring
on the ceiling. Two years later, new vacuum sources requiring
2,500 cfm are added to the processing areas, Figure 2b. Also,
a 3,500 cfm exhaust system is added to a cooler room to remove
carbon dioxide.

After
these modifications, 18,000 cfm are exhausted at other locations
besides the picking and scalding rooms. A major portion of
this air comes from the evisceration room thus producing some
reverse flow in the plant and causing an even greater portion
of the air to flow into the picking and scalding rooms from
the shackling area, Figure 2b. Fan Maintenance The fans and
intakes in poultry meat plants are above the roof line and
are easily ignored because most of the attention is given
to t e operation on the floor ("out of sight, out of
mind"). However, fan capacity can be reduced by up to
50% when the guards and backdraft shutters are laden with
dust and feather material. Intakes can become completely plugged
by particulate emissions from nearby exhaust fans. Ventilation
equipment maintenance should be a routine task of the plant
maintenance crew.

Multi-Purpose
Rooms

Air distribution
should be taken into consideration when laying out processes
within the room. Sometimes, "clean operations" for
final product such as cutup and packaging are conducted in
the same room as "dirty operations" such as evisceration.
The "dirty operations" closer to the raw receiving
area emit bioaerosols that can move to and deposit onto clean
product. Thus, room air distribution is very important in
preventing unnecessary food contamination.

Fan
Mismatches

A food
manufacturing plant may have several types and sizes of fans
exhausting from the same room or adjoining rooms. High-pressure
power ventilators, tube-axial fans, centrifugal fans, and
vacuum systems sometimes operate in parallel with low-pressure
propeller fans. As a consequence, weaker exhaust fans operate
at reduced efficiency and air flow. Also, relatively moist
air condenses on the inside of fan housings as air flow decreases.
Additionally, air flow from areas with contamination sources
to clean areas such as meat packaging may be created due to
reverse flow. This increases product contamination and decreases
food safety. In one case, about 5,000 cfm of air actually
reversed through a large, belt-driven, exhaust fan running
at slow speed in a feather wash room, Figure 3. This occurred
because, in addition to strong exhaust fans in adjoining rooms,
a furnace with a high speed centrifugal fan exhausted air
from the same room and blew hot air into the adjoining rooms
via ductwork. The negative static pressure created by the
furnace fan was felt by the slow moving fan as excessive back
pressure. The airflow through the weak exhaust fan became
positive again after the furnace was shut off. To correct
this situation, weak fans should be replaced with stronger
or higher pressure fans. Or the speed of the weak fan should
be increased. In this particular case, the supply air for
the furnace could have been taken from another room.

Figure3. Example of fan mismatch in feather wash room.

Effects
of Wind Pressure

Wind
blowing into a large opening such as open doors or windows
can pressurize a room causing undesired flow of air. In one
case, air flowed through door cracks and other openings from
a compressor and refrigeration room into a meat processing
room when an overhead door was opened to "cool the compressors,"
Figure 4a. The door was opened to an oncoming 12 mph wind
even though the compressor room had its own exhaust ventilation
system. Upon shutting the overhead door, the pressure in the
compressor room became negative compared to that of the processing
room and air flowed from the processing room to the compressor
room, as desired, to keep contaminants away from clean product,
Figure 4b.

Figure4. Effect of wind pressure on leaks into clean product
area of the plant with garage door open (a) and closed (b).

In another
case, an overhead door in the picking room facing an 8-mph
wind was opened on a hot summer day, Figure 5a. The resulting
18,000 cfm of air flowing inward through this door created
high humidity and airborne microbial concentrations in the
adjoining evisceration and processing room. The picking room
was equipped with large exhaust fans, but the wind pressurized
the "dirty" room in such as a way as to induce airflow
into the "clean" room through some of the line openings
between the two rooms, Figure 5a. Shutting the overhead garage
door allowed the exhaust fans to create the negative pressure
required to draw air through all openings from the evisceration
and packing room, Figure 5b.

Figure 5. Effect of wind pressure on airflow between dirty
and clean rooms with garage door open (a) and closed (b).

Summary

The emission
of airborne particles with pathogenic and spoilage microorganisms
in poultry slaughtering and processing plants can create
high airborne concentrations. It is important to keep these
unwanted bioaerosols from processing and packing areas to
assure product quality and safety and the health and well-being
of plant workers. The design of ventilation systems is challenging
because large airflows occur through shackle line openings
between rooms and from the outdoors. However, careful design
and maintenance of the ventilation system can prevent migration
of airborne contamination from reaching clean areas of the
plant.

Cooperative
Extension work in Agriculture and Home Economics, state of Indiana,
Purdue University, and U.S. Department of Agriculture cooperating;
H. A. Wadsworth, Director, West Lafayette, IN. Issued in furtherance
of the acts of May 8 and June 30, 1914. The Purdue University
Cooperative Extension Service is an equal opportunity/equal
access institution.